O ring seals at end of shaft, failed after a couple weeks.
Blackburn quickly sent a replacement part, a pump head, nice but didn't fix it.
Bought O rings from an industrial supply house, now pump works sort of OK.
Used this pump 2-3x / week for almost a year and something inside the pump body broke so that it now doesn't push any air. I've had cheaper pumps under the same conditions last far longer. Save your money.
To the person who had something go wrong with their pump. Just call Blackburn, they have a lifetime warranty, they'll ship you a new pump. Can't get better than that.